While there are a few posts here indicating success with just using an OEM native 9mm barrel with the P226, I would be inclined to go with a conversion barrel. Some .40 mags/pistols may function OK. some may not. For SD, I'd go with conversion barrel and 9mm mags. Regardless, test the hell out of it before carrying.

I'm not opposed to using the native OEM 9mm barrel on P239 .40's. Mine functions 100% with both .40 and 9 mm mags. Many others have reported the same.

______________________An expert is one who knows more and more about less and less until he knows absolutely everything about nothing. --Nicholas Murray Butler

Would someone put a caliper on a SIG P226 OEM .40 barrel and a SIG P226 OEM 9 barrel? Please? If an OEM 9mm barrel would fit in a .40 P226 slide, why would SIG sell a 9mm conversion kit that includes a slide?